Composition for cleaning inkjet head

Abstract

To provide a cleaning composition excellent in cleaning performance for coating films and excellent in component adaptability.SOLUTION: A cleaning composition for inkjet head contains a solvent (A) and water. The solvent (A) has a dipole moment determined by density functional theory at 25°C of 5.0 D or more. The water content in the cleaning composition is 30 mass% or more.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a cleaning composition for an inkjet head. [Background technology]

[0002] Cleaning compositions are widely used with various compositions adjusted in consideration of the cleaning effect as well as the required properties according to the type of object to be cleaned, the form of the composition, the method of use, etc. Examples of such cleaning compositions include articles using pigment dispersions. A pigment dispersion is composed of a pigment having various functionalities and a medium in which the pigment is dispersed. A pigment dispersion is a mixture of a solid pigment and a liquid medium, and a polymer is often used to disperse the pigment in the medium. In addition, a polymer other than the polymer for dispersing the pigment may be used to impart various properties. Therefore, even if the pigment dispersion is stable immediately after its production, the pigment dispersion state may change to an irreversible state due to the passage of time or the application of heat, etc., due to the precipitation or aggregation of the pigment, the adsorption of the pigment to the member to which the pigment dispersion is attached, and further due to the drying of the pigment and the fixation due to the presence of the above-mentioned polymer. While this irreversible state change is sometimes used favorably as a function of the pigment dispersion, it is often seen to have a secondary effect that is not intended by the designer of the pigment dispersion, and there are many cases in which this has caused losses in industrial use.

[0003] One example is inkjet recording ink. If inkjet recording ink is left unused, the ink components will aggregate in the ejection nozzle, causing solid matter to adhere to the vicinity of the ejection nozzle. This adhesion of solid matter not only induces ejection defects such as deflected ejection, but also causes nozzle clogging if left unused, which may force the replacement of expensive inkjet heads. There are many reasons why ink components aggregate, including settling due to the high specific gravity of pigments and an increase in ink concentration due to the drying of the ink medium. When inkjet recording inks are used in a variety of industrial fields, adhesion of ink solids to the vicinity of the ejection nozzle and clogging of the nozzles reduces the production speed of the printing machine and increases running costs, and is one of the obstacles to the widespread use of inkjet recording inks. In response to this problem, various studies have been carried out on cleaning solutions for inkjet heads.

[0004] For example, Patent Document 1 describes a cleaning liquid for aqueous ink containing a pigment and a water-insoluble polymer, which has excellent cleaning properties for aqueous ink containing a pigment and a water-insoluble polymer, and a method for cleaning aqueous ink using the cleaning liquid, the cleaning liquid containing a surfactant, a water-soluble organic solvent containing diethylene glycol monoisopropyl ether, and water, the surfactant containing one or more selected from acetylene glycol or an ethylene oxide adduct thereof, and a polyethylene glycol alkyl ether having an alkyl group having 8 or more carbon atoms, or a polyethylene glycol aryl ether having an aryl group having 6 or more carbon atoms, and the content of the water-soluble organic solvent in the cleaning liquid is within a predetermined range, and a method for cleaning aqueous ink using the cleaning liquid. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2018-104637 A Summary of the Invention [Problem to be solved by the invention]

[0006] In the technology of Patent Document 1, an attempt is made to improve the washability of the ink in the inkjet head by applying a cleaning liquid containing a surfactant and an amphipathic organic solvent. However, in such technology, there is a trade-off between the washability of the ink and the resistance of the inkjet head components. The resistance of the inkjet head components means that the surfactant or amphipathic organic solvent acts to cause deformation of the components of the inkjet head, such as adhesives and packings, by swelling or dissolution, causing the shape of the inkjet head to become distorted, or the components of the inkjet head to peel off. When a cleaning liquid for an ink with low compatibility of such component resistance is applied, the inkjet head may become unusable in a much shorter period than expected. Therefore, there is a demand for both excellent washability of the coating film derived from the ink attached to components such as the inkjet head and excellent compatibility with the components. An object of the present invention is to provide a cleaning composition which has excellent coating film cleaning properties, thereby achieving excellent ejection recovery of an inkjet head, and which also has excellent compatibility with components. [Means for solving the problem]

[0007] The present inventors have found that the above problems can be solved by providing an inkjet head cleaning composition containing a solvent and water, wherein the solvent has a dipole moment of 5.0 D or more at 25° C. as determined by a density functional method, and the content of water in the inkjet head cleaning composition is 30 mass % or more.

[0008] That is, the present invention provides a cleaning composition for an inkjet head, comprising a solvent (A) and water, the dipole moment of the solvent (A) at 25° C. as determined by a density functional method is 5.0 D or more; The cleaning composition for an inkjet head has a water content of 30% by mass or more. Effect of the Invention

[0009] The present invention can provide a cleaning composition for an inkjet head which has excellent coating film cleaning properties, and therefore excellent ejection recovery properties for an inkjet head, and which also has excellent compatibility with components. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] [Cleaning composition] The cleaning composition of the present invention is a cleaning composition containing a solvent (A) and water, wherein the dipole moment of the solvent (A) at 25°C determined by a density functional method is 5.0 D or more, and the content of water in the cleaning composition is 30 mass% or more. The cleaning composition of the present invention is preferably a cleaning composition for inkjet heads.

[0011] The cleaning composition of the present invention has excellent coating film cleaning properties and also has excellent compatibility with components. The reason for this is not clear, but is thought to be as follows. The solvent (A) contained in the cleaning composition of the present invention has a dipole moment of 5.0 D or more at 25° C. as determined by density functional theory, and has a large electrical bias in the molecule. Therefore, it is likely to orient toward the hydrophilic functional group portion of the polymer constituting the coating film, thereby enhancing the wettability of the cleaning composition of the present invention to the polymer. In addition, due to the electrical bias in the molecules of the solvent (A), the distance between the molecules of the solvent (A) is likely to be close and stable. For this reason, it is believed that the solvent (A) molecules are likely to form chains with each other starting from the solvent (A) molecules oriented to the hydrophilic functional groups of the polymer that constitutes the coating film, and the solvent (A) gathers near the hydrophilic functional groups. Furthermore, since the solvent (A) has a dipole moment of 5.0D or more at 25°C and is highly soluble in water, after gathering near the hydrophilic functional groups of the polymer, it is likely to attract water and move the polymer into water, which is believed to improve the peelability of the coating film from the object to be washed and improve the excellent washability of the coating film. Furthermore, even if the coating film contains a pigment, the cleaning composition of the present invention acts on the polymer that constitutes the coating film as described above, and is therefore thought to improve the removability of the pigment-containing coating film from the object to be cleaned, thereby improving the excellent cleaning properties of the pigment-containing coating film. Furthermore, the cleaning composition of the present invention has a water content of 30% by mass or more, and the organic solvent content can be reduced, so that the composition has excellent compatibility with components. Due to these actions, it is believed that by using the cleaning composition of the present invention on a coating film attached to an inkjet head, it is possible to achieve both ejection recovery properties based on excellent cleanability and excellent compatibility with components.

[0012] <Solvent (A)> The cleaning composition of the present invention contains a solvent (A) (hereinafter, also referred to as "solvent (A)") from the viewpoint of improving the peelability of the coating film and thereby improving the cleaning properties, and the dipole moment of the solvent (A) at 25°C as determined by a density functional method is 5.0 D or more. In the present invention, the dipole moment is measured at 25° C. As described in the Examples, the dipole moment is calculated by the density functional method using quantum chemistry calculation software TURBOMOLE Ver. 7.7, BP86 as the functional, and def-TZVP as the basis function. The unit of the dipole moment is "D (Debye)". The dipole moment of the solvent (A) is preferably 5.2D or more, more preferably 5.4D or more, and even more preferably 5.6D or more from the viewpoints of improving the peelability of the coating film and thereby improving the cleaning ability, and from the viewpoints of improving the compatibility with components, and from the same viewpoints as above, it is preferably 6.5D or less, more preferably 6.3D or less, and even more preferably 6.1D or less. The solvent (A) may be used alone or in combination of two or more.

[0013] From the viewpoint of improving the peelability and cleaning properties of the coating film, the solvent (A) is preferably one or more selected from the group consisting of cyclic carbonates and cyclic sulfones, and more preferably one or more selected from the group consisting of propylene carbonate (dipole moment: 5.64 D), ethylene carbonate (dipole moment: 5.41 D), and sulfolane (dipole moment: 5.39 D). Propylene carbonate, ethylene carbonate, and sulfolane, which are preferably used in the cleaning composition of the present invention, have a dipole moment of 5.0 D or more and are cyclic organic solvents, so they are thought to easily enter the gaps in the polymer that constitutes the coating film, and have the effect of increasing the swelling property of the polymer. On the other hand, propylene carbonate, ethylene carbonate, and sulfolane are water-soluble, so after entering the gaps in the polymer, they are thought to easily draw in water, improving the peelability of the coating film from the object to be cleaned and improving the excellent cleaning property of the coating film. From the viewpoint of improving the peelability and cleaning properties of the coating film, the solvent (A) is more preferably at least one selected from the group consisting of propylene carbonate and ethylene carbonate, and even more preferably propylene carbonate or a mixture of propylene carbonate and ethylene carbonate.

[0014] When the solvent (A) is a mixture of propylene carbonate and ethylene carbonate, the mass ratio of the ethylene carbonate content to the propylene carbonate content in the cleaning composition of the present invention [ethylene carbonate / propylene carbonate], from the viewpoint of achieving both cleaning performance and component compatibility, is preferably more than 0 and is preferably 5 or less, more preferably 4 or less, even more preferably 3 or less, still more preferably 2 or less, still more preferably 1 or less, still more preferably 0.7 or less, still more preferably 0.5 or less, and still more preferably 0.3 or less.

[0015] The content of the solvent (A) in the cleaning composition of the present invention is, from the viewpoint of improving the peelability of the coating film and thereby improving cleaning properties, preferably 5 mass % or more, more preferably 8 mass % or more, even more preferably 10 mass % or more, still more preferably 15 mass % or more, and still more preferably 17 mass % or more, and from the viewpoint of improving component compatibility, preferably 65 mass % or less, more preferably 60 mass % or less, even more preferably 55 mass % or less, still more preferably 45 mass % or less, still more preferably 40 mass % or less, still more preferably 30 mass % or less, and still more preferably 20 mass % or less.

[0016] <Solvent (B)> From the viewpoint of improving the dispersibility of the coating film peeled off from the object to be cleaned and thereby improving the cleaning properties, the cleaning composition of the present invention preferably contains, in addition to the solvent (A), an organic solvent (B) having one or more groups selected from the group consisting of a hydroxy group and a polyoxyalkylene group (hereinafter also referred to as "solvent (B)"). The solvent (B) may be used alone or in combination of two or more. Specific examples of the solvent (B) include ethylene glycol, diethylene glycol, polyoxyalkylene phenyl ether, and polyoxyalkylene benzyl ether. The solvent (B) preferably contains one or more solvents (B1) (hereinafter also simply referred to as "solvent (B1)") selected from the group consisting of ethylene glycol, diethylene glycol, polyoxyalkylene phenyl ether, and polyoxyalkylene benzyl ether. When the cleaning composition of the present invention contains solvent (B1) in addition to solvent (A), it is believed that the strong polarity of the alkylene group of solvent (B1) and the oxygen atoms present at both ends or between the alkylene group causes solvent (A) to disperse the coating film peeled off from the object to be cleaned in the cleaning composition of the present invention containing water, and as a result, it is believed that the cleaning properties of the coating film are further improved. Of these, from the viewpoint of improving the dispersibility of the coating film peeled off from the object to be cleaned and thereby improving the cleanability, the solvent (B1) is preferably at least one selected from the group consisting of polyoxyalkylene phenyl ethers and polyoxyalkylene benzyl ethers.

[0017] From the viewpoint of improving the dispersibility of the coating film peeled off from the object to be cleaned and improving the cleanability, the polyoxyalkylene group of the polyoxyalkylene phenyl ether preferably contains a unit derived from an alkylene oxide having from 2 to 4 carbon atoms. Examples of the alkylene oxide include ethylene oxide, propylene oxide, butylene oxide, etc., and are preferably one or more selected from the group consisting of ethylene oxide and propylene oxide, more preferably contain at least ethylene oxide, and even more preferably are ethylene oxide. In other words, the polyoxyalkylene group of the polyoxyalkylene phenyl ether more preferably contains at least a polyoxyethylene group, and even more preferably is a polyoxyethylene group. Specifically, the polyoxyalkylene phenyl ether is preferably at least one selected from the group consisting of polyoxyethylene phenyl ether and polyoxypropylene phenyl ether, and among these, polyoxyethylene phenyl ether is more preferable. The average number of moles of alkylene oxide added in the polyoxyalkylene group of the polyoxyalkylene phenyl ether is, from the viewpoint of improving the dispersibility of the coating film peeled off from the object to be cleaned and thereby improving the cleanability, preferably 2 or more, more preferably more than 2, even more preferably 3 or more, and is preferably 10 or less, more preferably 8 or less, even more preferably 6 or less.

[0018] From the viewpoint of improving the dispersibility of the coating film peeled off from the object to be cleaned and improving the cleanability, the polyoxyalkylene group of the polyoxyalkylene benzyl ether preferably contains a unit derived from an alkylene oxide having from 2 to 4 carbon atoms. Examples of the alkylene oxide include ethylene oxide, propylene oxide, butylene oxide, etc., and are preferably one or more selected from the group consisting of ethylene oxide and propylene oxide, more preferably contain at least ethylene oxide, and even more preferably are ethylene oxide. In other words, the polyoxyalkylene group of the polyoxyalkylene benzyl ether more preferably contains at least a polyoxyethylene group, and even more preferably is a polyoxyethylene group. Specifically, the polyoxyalkylene benzyl ether is preferably at least one selected from the group consisting of polyoxyethylene benzyl ether and polyoxypropylene benzyl ether, and among these, polyoxyethylene benzyl ether is more preferred. The average number of moles of alkylene oxide added in the polyoxyalkylene group of the polyoxyalkylene benzyl ether is preferably 2 or more, and is preferably 10 or less, more preferably 8 or less, and even more preferably 6 or less, from the viewpoint of improving the dispersibility of the coating film peeled off from the object to be cleaned and thereby improving the cleanability.

[0019] From the viewpoint of improving the dispersibility of the coating film peeled off from the object to be cleaned and thereby improving the cleanability, the content of solvent (B1) in component (B) is preferably 70 mass% or more, more preferably 80 mass% or more, even more preferably 90 mass% or more, still more preferably 95 mass% or more, still more preferably 97 mass% or more, and is preferably 100 mass% or less, and even more preferably 100 mass%.

[0020] The content of component (B) in the cleaning composition of the present invention is preferably 0.5% by mass or more, more preferably 1% by mass or more, and even more preferably 2% by mass or more, from the viewpoint of improving the dispersibility of the coating film peeled off from the object to be cleaned and thereby improving the cleaning performance, and from the viewpoint of improving the compatibility with components, it is preferably 50% by mass or less, more preferably 40% by mass or less, even more preferably 30% by mass or less, still more preferably 20% by mass or less, and even more preferably 10% by mass or less.

[0021] The content of the solvent (B1) in the cleaning composition of the present invention is preferably 0.5% by mass or more, more preferably 1% by mass or more, and even more preferably 2% by mass or more, from the viewpoint of improving the dispersibility of the coating film peeled off from the object to be cleaned and thereby improving the cleaning ability, and from the viewpoint of improving the compatibility with components, it is preferably 50% by mass or less, more preferably 40% by mass or less, even more preferably 30% by mass or less, still more preferably 20% by mass or less, and even more preferably 10% by mass or less.

[0022] The mass ratio of the content of solvent (B) to the content of solvent (A) in the cleaning composition of the present invention [solvent (B) / solvent (A)], from the viewpoint of improving the cleanability of the coating film, is preferably 0.05 or more, more preferably 0.07 or more, even more preferably 0.10 or more, and is preferably 3.0 or less, more preferably 2.5 or less, even more preferably 2.0 or less, still more preferably 1.5 or less, still more preferably 1.0 or less, still more preferably 0.9 or less, still more preferably 0.7 or less, still more preferably 0.5 or less, and still more preferably 0.3 or less.

[0023] (Other solvents) The cleaning composition of the present invention may contain other solvents than the solvents (A) and (B) to the extent that the effect of the present invention is not impaired. Examples of such other solvents include gamma-butyrolactone (dipole moment: 4.69D), 2-pyrrolidone (dipole moment: 4.16D), dimethylsulfoxide (dipole moment: 4.10D), dimethylformamide (dipole moment: 4.06D), N-methylpyrrolidone (dipole moment: 3.99D), tetrahydrofuran (dipole moment: 1.92D), cyclohexane (dipole moment: 0.00D), and benzene (dipole moment: 0.00D).

[0024] The content of solvents other than the solvents (A) and (B) in the cleaning composition of the present invention is preferably 10 mass % or less, more preferably 5 mass % or less, even more preferably 3 mass % or less, and still more preferably 0 mass %, from the viewpoint of improving the cleanability of the coating film and improving the compatibility with components.

[0025] <Water> The cleaning composition of the present invention contains water from the viewpoint of improving the cleaning property of the coating film and from the viewpoint of improving the compatibility with components. The water may be any of tap water, ion-exchanged water, ultrafiltered water, RO water, and distilled water, but from the viewpoint of improving the cleaning property of the coating film, it is preferable to use at least one type of water selected from the group consisting of ion-exchanged water, ultrafiltered water, RO water, and distilled water.

[0026] The water content in the cleaning composition of the present invention, from the viewpoint of improving the cleaning properties of the coating film and improving compatibility with components, is 30% by mass or more, preferably 35% by mass or more, more preferably 40% by mass or more, even more preferably 45% by mass or more, still more preferably 50% by mass or more, still more preferably 55% by mass or more, still more preferably 60% by mass or more, and is preferably 90% by mass or less, more preferably 85% by mass or less, and even more preferably 80% by mass or less.

[0027] The mass ratio of the content of the solvent (A) to the content of water in the cleaning composition of the present invention [solvent (A) / water] is, from the viewpoint of improving the cleanability of the coating film, preferably 0.05 or more, more preferably 0.07 or more, even more preferably 0.10 or more, still more preferably 0.15 or more, and still more preferably 0.20 or more, and from the viewpoint of improving component compatibility, is preferably 3.0 or less, more preferably 2.0 or less, even more preferably 1.5 or less, still more preferably 1.0 or less, still more preferably 0.70 or less, still more preferably 0.50 or less, and still more preferably 0.30 or less.

[0028] In addition to the above-mentioned components, the cleaning composition of the present invention may contain various commonly used additives such as a pH adjuster, an antifoaming agent, an antiseptic, an antifungal agent, and an antirust agent. The cleaning composition of the present invention does not contain any pigment or polymer. From the viewpoint of dispersibility of the pigment and the polymer, it is preferable that the cleaning composition of the present invention does not contain an acid or an oxidizing agent. The cleaning composition of the present invention can be obtained by mixing and stirring the solvent (A), water, and, if necessary, the solvent (B), the other solvents described above, and the additives.

[0029] (Cleaning method) The cleaning composition of the present invention is preferably used for cleaning a coating film attached to an object to be cleaned. The object to be cleaned is preferably an inkjet head. That is, the cleaning method using the cleaning composition of the present invention is preferably a method for cleaning an inkjet head using the cleaning composition. The cleaning method using the cleaning composition of the present invention is preferably a method of contacting the cleaning composition with the coating film attached to the object to be cleaned. Examples of the contacting method include immersion method, spraying method, coating method, and stirring method. In addition, the method of soaking the cleaning composition of the present invention into a liquid-absorbent wiping member such as a nonwoven fabric and wiping and cleaning the surface of the object to be cleaned is preferable as a method of removing a coating film that is firmly attached.

[0030] [Uses of the cleaning composition of the present invention] The cleaning composition of the present invention has excellent cleaning properties for coating films and excellent compatibility with components, and is therefore preferably used, for example, as a cleaning agent for water-based inks containing polymers. In the present invention, "water-based" means that water accounts for the largest proportion by mass of the medium in which the polymer is dispersed. In this case, even if the polymer is a water-insoluble polymer, it can be cleaned well. In the present invention, the term "water-insoluble polymer" means that when a polymer that has been dried at 105°C for 2 hours and has reached a constant weight is dissolved in 100 g of water at 25°C until saturation is reached, the amount of dissolution is 10 g or less, preferably 5 g or less, more preferably 1 g or less. When the water-insoluble polymer is an anionic polymer, the amount of dissolution is the amount of dissolution when the anionic group of the polymer is 100% neutralized with sodium hydroxide. When the water-insoluble polymer is a cationic polymer, the amount of dissolution is the amount of dissolution when the cationic group of the polymer is 100% neutralized with hydrochloric acid.

[0031] When the cleaning composition of the present invention is used as a cleaning agent for an aqueous ink containing a polymer and water (hereinafter, also simply referred to as "aqueous ink"), it is preferably used as a cleaning agent for an aqueous ink for flexographic printing, gravure printing, or inkjet recording, and more preferably used as a cleaning agent for an aqueous ink for inkjet recording. The term "recording" is a concept including printing and printing for recording characters or images. When the cleaning composition of the present invention is used as a cleaning agent for removing a coating film of a water-based ink for ink-jet printing adhered to an ink-jet head, the cleaning composition of the present invention exerts its cleaning effect and can improve ejection recovery. When the cleaning composition of the present invention is used as a cleaning agent for water-based inks for inkjet recording, it can also be used to clean an inkjet recording device using the water-based inks for inkjet recording, and tools for maintaining the recording device. Among these, it is preferable to apply it to cleaning an inkjet recording device, and more preferable to apply it to cleaning an inkjet head. Specifically, it can be used to clean the ink ejection port of an inkjet head, the area near the ink ejection port, and the ink supply path from an ink tank or ink cartridge to the ink ejection port of an inkjet recording device. More specifically, it can be suitably used as a cleaning agent (spray liquid, wiping liquid) for water-based inks for inkjet recording that are attached to a nozzle plate having a large number of ejection nozzle holes provided in an inkjet head of each color ink. That is, the cleaning composition of the present invention can be preferably used as a cleaning composition for an inkjet head.

[0032] <Water-based ink> The water-based ink that is the target of the cleaning composition of the present invention contains a polymer and water. The water-based ink may be a so-called undercoat liquid and / or overcoat liquid. The water-based ink may further contain a pigment in addition to the polymer and water. That is, the coating film to be cleaned by the cleaning composition of the present invention contains at least a component derived from the polymer derived from the water-based ink, and preferably contains a component derived from the polymer and a component derived from the pigment.

[0033] 〔polymer〕 The polymer contained in the aqueous ink that is the target of the cleaning composition of the present invention is preferably one that is contained for at least one of the following functions: a function as a pigment dispersant that exerts a pigment dispersing effect, or a function as a fixing agent for the print medium. The polymer that functions as a pigment dispersant (hereinafter also referred to as a "pigment dispersing polymer") is preferably a water-insoluble polymer from the viewpoints of the dispersion stability and ejection recovery properties of the ink. From the viewpoint of the dispersion stability and ejection recovery of the ink, preferred examples of the pigment dispersion polymer include at least one selected from the group consisting of polyester resins, polyurethane resins, and vinyl resins. Among these, at least one selected from the group consisting of polyester resins and vinyl resins is more preferred, and polyester resins are even more preferred.

[0034] The polyester resin can be obtained by polycondensation of an alcohol component and a carboxylic acid component. The alcohol component can be an aromatic or aliphatic polyol, and preferably contains an aromatic diol such as an alkylene oxide adduct of bisphenol A. The carboxylic acid component can be, for example, an aromatic dicarboxylic acid, an aliphatic dicarboxylic acid, or a polyvalent carboxylic acid having three or more valences, and preferably contains an aliphatic dicarboxylic acid such as fumaric acid.

[0035] The vinyl resin can be obtained by addition polymerization, by a known method, of a monomer mixture containing an ionic monomer such as acrylic acid or methacrylic acid and one or more selected from a hydrophobic monomer such as an alkyl (meth)acrylate or an aromatic group-containing monomer, and a hydrophilic nonionic monomer such as a polyalkylene glycol (meth)acrylate. Among these, the water-based ink is preferably one in which a pigment is dispersed in a water-insoluble polymer having an anionic group such as a carboxy group, from the viewpoints of dispersion stability and ejection recovery of the ink.

[0036] From the viewpoint of the dispersion stability and ejection recovery of the ink, the water-based ink preferably contains the pigment in the form of water-insoluble polymer particles containing the pigment (hereinafter, also simply referred to as "pigment-containing polymer particles") using the above-mentioned water-insoluble polymer as the pigment dispersion polymer. The pigment-containing polymer particles are only required to be particles formed by the pigment and the water-insoluble polymer, and are formed by adsorbing the water-insoluble polymer to the pigment in the water-based ink. Examples of the particle form include a particle form in which the pigment is encapsulated in the polymer, a particle form in which the pigment is uniformly dispersed in the polymer, a particle form in which the pigment is exposed on the surface of the polymer particle, and the like, and mixtures thereof are also included.

[0037] The polymer that functions as a fixing agent for print media (hereinafter also referred to as a "fixing aid polymer") is preferably a water-insoluble polymer from the viewpoint of imparting higher fixing properties to printed matter. Preferred examples of the fixing aid polymer include, from the viewpoint of imparting higher fixing property to printed matter, one or more selected from the group consisting of polyester resins, acrylic resins, styrene / (meth)acrylic resins, styrene resins, styrene / butadiene resins, butadiene resins, vinyl chloride resins, vinyl acetate resins, and polyurethane resins. Among these, more preferred are one or more selected from the group consisting of polyester resins, acrylic resins, and styrene / acrylic resins, and even more preferred are polyester resins. The fixing aid polymers may be used alone or in combination of two or more.

[0038] From the viewpoints of fixation to a print medium and abrasion resistance of a printed matter, the fixing aid polymer is preferably water-insoluble polymer particles containing no pigment, and more preferably polyester resin particles containing no pigment. The polyester resin constituting the polyester resin particles not containing a pigment can be obtained by polycondensation of an alcohol component and a carboxylic acid component. The alcohol component includes aromatic or aliphatic polyols, and preferably includes aromatic diols such as alkylene oxide adducts of bisphenol A. The carboxylic acid component includes aromatic dicarboxylic acids, aliphatic dicarboxylic acids, and polycarboxylic acids having three or more valences, and preferably includes aromatic dicarboxylic acids, aliphatic dicarboxylic acids, and polycarboxylic acids having three or more valences.

[0039] From the viewpoint of handling, it is preferable to use water-insoluble polymer particles that do not contain pigments as a dispersion, and those synthesized by emulsion polymerization or the like may be used, or commercially available products may be used. Commercially available dispersions of water-insoluble polymer particles that do not contain pigments include, for example, acrylic resins such as "Neocryl A1127" (manufactured by DSM NeoResins, anionic self-crosslinking water-based acrylic resin), "Joncryl 390" (manufactured by BASF Japan Co., Ltd.), styrene / acrylic resins such as "Joncryl 7100", "Joncryl 734", and "Joncryl 538" (all manufactured by BASF Japan Co., Ltd.), styrene / butadiene resins such as "SR-100" and "SR102" (all manufactured by Nippon A&L Co., Ltd.), vinyl chloride resins such as "Vinyblan 701" (manufactured by Nissin Chemical Industry Co., Ltd.), and polyurethane resins such as "WBR-2018" and "WBR-2000U" (all manufactured by Taisei Fine Chemical Co., Ltd.).

[0040] When the water-based ink contains pigment-containing polymer particles, the weight-average molecular weight of the water-insoluble polymer constituting the particles is preferably 5,000 or more, more preferably 7,000 or more, even more preferably 10,000 or more, and preferably 100,000 or less, more preferably 50,000 or less, even more preferably 30,000 or less. When the water-based ink contains water-insoluble polymer particles that do not contain a pigment, the weight average molecular weight of the water-insoluble polymer that constitutes the particles is preferably 5,000 or more, more preferably 7,000 or more, even more preferably 10,000 or more, and preferably 100,000 or less, more preferably 50,000 or less, even more preferably 30,000 or less. The weight average molecular weight of the water-insoluble polymer can be measured by gel permeation chromatography, and the specific measurement method can be the method described in the Examples.

[0041] From the viewpoint of improving the removability of the coating film and further improving the cleaning property, the acid value of the polymer is preferably 5 mgKOH / g or more, more preferably 10 mgKOH / g or more, and further preferably 20 mgKOH / g or more. Since the higher the acid value of the polymer, the better the removability of the coating film by the cleaning agent of the present invention, there is no particular upper limit for the acid value of the polymer.

[0042] [Pigments] The pigment contained in the water-based ink to which the cleaning composition of the present invention is applied may be either an inorganic pigment or an organic pigment, and may also be used in combination with an extender pigment, if necessary. Examples of inorganic pigments include carbon black and metal oxides. In the case of black ink, carbon black is preferred. Examples of carbon black include furnace black, lamp black, acetylene black, and channel black. In the case of white ink, examples of metal oxides include titanium dioxide, zinc oxide, silica, alumina, and magnesium oxide. Examples of organic pigments include azo pigments, diazo pigments, phthalocyanine pigments, quinacridone pigments, isoindolinone pigments, dioxazine pigments, perylene pigments, perinone pigments, thioindigo pigments, anthraquinone pigments, and quinophthalone pigments. In the achromatic ink, achromatic pigments such as white, black, and gray can be used, while in the chromatic ink, chromatic pigments such as yellow, magenta, cyan, red, blue, orange, and green can be used. Examples of the extender pigment include silica, calcium carbonate, and talc. The pigments can be used alone or in combination of two or more. The pigment may be contained in the water-based ink in the form of a self-dispersed pigment, a pigment dispersed with a dispersant, or water-insoluble polymer particles containing a pigment.

[0043] The water-based ink may further contain, as necessary, a neutralizing agent, an organic solvent, and a surfactant as components other than the polymer, water, and pigment. The water-based ink may also contain, as optional components, various additives such as a humectant, a wetting agent, a penetrating agent, a dispersant, a surfactant, a viscosity adjuster, a defoamer, a preservative, a fungicide, and a rust inhibitor.

[0044] The water-based ink can be obtained by mixing and stirring a pigment, a water-insoluble polymer, water, and, if necessary, a neutralizing agent, an organic solvent, a surfactant, and the like. In the case where the pigment-containing polymer particles are contained, the pigment-containing polymer particles may be blended in the aqueous ink after a dispersion of the pigment-containing polymer particles is obtained by dispersing the pigment, the water-insoluble polymer, and, if necessary, a neutralizing agent, a surfactant, and the like, using a known method.

[0045] The content of the water-insoluble polymer in the water-based ink is preferably 1 mass % or more, more preferably 3 mass % or more, and even more preferably 5 mass % or more, from the viewpoint of the dispersion stability and ejection recovery property of the ink, as well as the fixation to the printing medium and the abrasion resistance of the printed matter, and from the viewpoint of the viscosity of the ink, it is preferably 20 mass % or less, more preferably 15 mass % or less, and even more preferably 10 mass % or less. When the water-based ink contains a pigment, the content of the pigment in the water-based ink is preferably 1% by mass or more, more preferably 2% by mass or more, and even more preferably 3% by mass or more, from the viewpoint of the print density of the printed matter, and is preferably 15% by mass or less, more preferably 10% by mass or less, even more preferably 8% by mass or less, and even more preferably 6% by mass or less, from the viewpoint of the viscosity of the ink and the abrasion resistance of the printed matter. In addition, when the water-based ink contains pigment-containing polymer particles and pigment-free polymer particles, the content of the water-insoluble polymer is the total amount of the water-insoluble polymer contained in the pigment-containing polymer particles and the pigment-free polymer particles. From the viewpoints of dispersion stability of the ink and abrasion resistance of printed matter, the water content in the water-based ink is preferably 35% by mass or more, more preferably 40% by mass or more, even more preferably 45% by mass or more, and is preferably 80% by mass or less, more preferably 75% by mass or less, even more preferably 70% by mass or less.

[0046] The cleaning method using the cleaning composition of the present invention as a cleaning agent for water-based ink is preferably a method of contacting the cleaning composition with the coating film of the object to be cleaned that has been adhered to the surface by water-based ink, as described above, and examples of the contacting method include the immersion method, spraying method, coating method, stirring method, etc. Examples of the cleaning method include a method of soaking a liquid-absorbent wiping member such as a nonwoven fabric with the cleaning composition of the present invention and wiping off the coating film attached to the inkjet nozzle surface or the inkjet nozzle outlet of an inkjet head; a method of cleaning the ink path in the printer before and after changing inks by repeatedly supplying the cleaning composition from a cartridge containing the cleaning composition using the printer's supply mechanism and discharge mechanism, and discharging the cleaning composition into the ink path using the printer's supply mechanism and discharge mechanism; a method of removing the coating film from the inkjet head, filling it with the cleaning composition, capping it, and storing it when the inkjet head is not used for a long period of time, etc. The wiping member is not particularly limited as long as it is liquid-absorbent, and examples of the wiping member include woven fabric, knitted fabric, nonwoven fabric, sponge, pulp, etc. In the cleaning method, from the viewpoint of exerting a more excellent cleaning power, the temperature when the cleaning composition is brought into contact is preferably 0°C or higher, more preferably 10°C or higher, and even more preferably 20°C or higher, and from the viewpoint of reducing energy, cleaning is preferably carried out at less than 100°C, more preferably 80°C or lower, even more preferably 70°C or lower, and even more preferably 50°C or lower.

[0047] The present invention is as follows: <1> The above embodiment is also included. <1> A cleaning composition comprising a solvent (A) and water, The dipole moment of the solvent (A) at 25°C as determined by density functional theory is 5. 0D or more, A cleaning composition, wherein the water content in the cleaning composition is 30 mass% or more. EXAMPLES

[0048] In the following Production Examples, Examples and Comparative Examples, "parts" and "%" are "parts by mass" and "% by mass" unless otherwise specified. The measurement and calculation methods for each physical property are as follows.

[0049] [Dipole moment of solvent at 25℃] The dipole moment of the solvent at 25°C was calculated using the quantum chemistry calculation software TURBOMOLE Ver.7.7, jointly developed by the Karlsruhe Research Center and the University of Karlsruhe, Germany, and was calculated using the density functional method. The functional used was BP86 and the basis set was def-TZVP. For those with multiple conformations, the calculation was performed with one conformation, using the most stable conformation in vacuum.

[0050] [Softening point of polyester resin] Using a flow tester "CFT-500D" (Shimadzu Corporation), 1 g of sample was heated at a temperature increase rate of 6°C / min, while applying a load of 1.96 MPa with the plunger, and extruding the sample from a nozzle with a diameter of 1 mm and a length of 1 mm. The plunger descent amount of the flow tester was plotted against the temperature, and the temperature at which half of the sample flowed out was taken as the softening point.

[0051] [Glass transition temperature of polyester resin] Using a differential scanning calorimeter "Pyris 6 DSC" (Perkin Elmer), 5 mg of sample was weighed into an aluminum pan, heated to 200°C, and cooled from that temperature to 0°C at a rate of 10°C / min. The sample was then heated at a rate of 10°C / min. The glass transition temperature was determined as the temperature at the intersection of an extension of the baseline below the maximum endothermic peak temperature and a tangent line showing the maximum slope from the rising part of the peak to the apex of the peak. In the case of the aqueous dispersion, the aqueous dispersion was freeze-dried at -10°C for 9 hours using a freeze-dryer "FDU-2100" manufactured by Tokyo Rikakikai Co., Ltd., to prepare a sample.

[0052] [Acid value of polyester resin] Measurement was performed according to the neutralization titration method described in JIS K 0070: 1992. However, the measurement solvent was changed from a mixed solvent of ethanol and ether to a mixed solvent of acetone and toluene [acetone:toluene=1:1 (volume ratio)].

[0053] [Weight average molecular weight (Mw) of polyester resin] The measurement was performed by the following gel permeation chromatography method. (1) Preparation of sample solution Polyester resin was dissolved in chloroform to a concentration of 0.5 g / 100 mL, and the resulting solution was filtered using a fluororesin filter "FP-200" (manufactured by Sumitomo Electric Industries, Ltd.) with a pore size of 2 μm to remove insoluble components, thereby preparing a sample solution. (2) Molecular weight measurement The following measuring equipment and analytical column were used, tetrahydrofuran was passed as a dissolving solution at a flow rate of 1 mL / min, and the column was stabilized in a thermostatic bath at 40°C. 100 μL of the sample solution was injected into the column and the measurement was performed. The weight-average molecular weight of the sample was measured using the following monodisperse polystyrene [monodisperse polystyrene manufactured by Tosoh Corporation; 2.63 × 10 3 , 2.06×10 4 , 1.02×10 5 (weight average molecular weight (Mw)), monodisperse polystyrene manufactured by GL Sciences Inc.; 2.10 × 10 3 , 7.00×103 , 5.04×10 4 (weight average molecular weight (Mw))] was used as a standard sample and calculation was performed based on a calibration curve prepared in advance. <Measurement conditions> Measuring device: "HLC-8220GPC" (Tosoh Corporation) Analytical column: "TSKgel GMHXL" + "TSKgel G3000HXL" (manufactured by Tosoh Corporation)

[0054] [Solid content concentration] 10.0 g of sodium sulfate was weighed out in a 30 mL polypropylene container (inner diameter 40 mm, height 30 mm) and 1.0 g of the sample was added thereto and mixed to obtain a mixture. The mixture was then weighed and maintained at 105°C for 2 hours to remove volatiles, and further left in the desiccator for 15 minutes, and the mass of the mixture after volatiles removal was measured. The mass of the mixture after volatiles removal minus the mass of sodium sulfate was determined as the solid content of the sample after volatiles removal, and this was divided by the mass of the sample before volatiles removal to obtain the solid content concentration (%).

[0055] [Average particle size of pigment-containing water-insoluble polymer particles and pigment-free water-insoluble polymer particles] The cumulant average particle size measured using a laser particle analysis system "ELS-8000" (cumulant analysis) manufactured by Otsuka Electronics Co., Ltd. was taken as the average particle size of the pigment-containing polymer particles or the pigment-free polymer particles. The measurement conditions were a temperature of 25°C, an angle between the incident light and the detector of 90°, and 100 integrations. The refractive index of water (1.333) was input as the refractive index of the dispersion medium. The measured concentration was 5×10 -3 It was done in %.

[0056] Production Examples 1-1 to 1-2 (Production of Polyester Resins P-1 to P-2) The raw material monomers (alcohol components and carboxylic acid components), esterification catalyst, and esterification promoter shown in Table 1 were mixed in the amounts shown in Table 1, and placed in a 10 L four-neck flask equipped with a thermometer, a stirrer, a downflow condenser, and a nitrogen inlet tube, and reacted in a mantle heater in a nitrogen atmosphere at 210°C for 10 hours, and then further reacted at -8.3 kPa (G) until the softening point reached the temperature shown in Table 1, to obtain polyester resins P-1 to P-2, respectively. The physical properties of the obtained polyester resins are shown in Table 1.

[0057] [Table 1]

[0058] Production Example 2-1 (Production of Water-Based Dispersion D-1 of Pigment-Containing Polyester Resin Particles) (1) Pigment dispersion process In a 2 L container, 66.7 g of polyester resin P-1 was dissolved as a pigment dispersion polymer in 156.4 g of methyl ethyl ketone (hereinafter referred to as "MEK"), and 5.36 g of 5N aqueous sodium hydroxide solution as a neutralizing agent and 430.0 g of ion-exchanged water were added thereto, and the degree of neutralization by sodium hydroxide relative to the acid value of polyester resin P-1 was adjusted to 85 mol%, and the mixture was stirred and mixed at 2,000 r / min for 15 minutes using a disperser blade at 10°C to 15°C. Next, 100.0 g of magenta pigment was added, and the mixture was stirred and mixed for 2 hours at 7,000 rpm using a disperser blade at 10° C. to 15° C. The resulting preliminary dispersion was filtered through a 150 mesh filter, diluted with 36.1 g of ion-exchanged water, and then dispersed 15 times at a pressure of 150 MPa using a Microfluidizer "M-110EH-30XP" (a high-pressure homogenizer manufactured by Microfluidics) to obtain a dispersion of pigment-containing polyester resin particles. (2) Concentration process The entire amount of the obtained dispersion of the pigment-containing polyester resin particles was placed in a 2L eggplant flask, ion-exchanged water was added so that the solid concentration was 16.0%, and the organic solvent was removed by holding for 3 hours at a pressure of 0.09 MPa (abs) in a warm bath adjusted to 32°C at a rotation speed of 50 r / min using a rotary distillation apparatus "Rotary Evaporator N-1000S" (Tokyo Rikakikai Co., Ltd.). Further, the warm bath was adjusted to 62°C, the pressure was reduced to 0.07 MPa (abs), and the mixture was concentrated until the solid concentration was 25.0%, to obtain a concentrate. The obtained concentrate was placed in a 500 mL angle rotor and centrifuged at 3,660 r / min for 20 minutes using a high-speed refrigerated centrifuge "himac CR22G" (manufactured by Hitachi Koki Co., Ltd., set temperature 20°C). The liquid layer was then filtered through a membrane filter "Minisart" (manufactured by Sartorius) with a pore size of 5 μm to obtain an aqueous dispersion 1 of pigment-containing polyester resin particles. Ion-exchanged water was added so that the solids concentration of the obtained aqueous dispersion 1 became 22.0%, and 0.76 g of "Proxel (registered trademark) LV (S)" (manufactured by Lonza Japan Co., Ltd.: preservative, active content 20%) was further added and stirred at 70°C for 2 hours. After cooling to 25°C, it was filtered through the 5 μm pore size filter, and further ion-exchanged water was added to obtain aqueous dispersion D-1 of pigment-containing polyester resin particles (solids concentration 22.0%). The average particle size of the pigment-containing polyester resin particles in aqueous dispersion D-1 was 130 nm.

[0059] Production Example 3-1 (Production of Water-Based Dispersion d-1 of Pigment-Free Polyester Resin Particles) In a four-neck flask equipped with a nitrogen inlet tube, a reflux condenser, a stirrer, and a thermocouple, polyester resin P-2 as a fixing aid polymer and methyl ethyl ketone (MEK) as an organic solvent were placed in the formulation shown in Table 2, and dissolved in MEK at 25°C. Next, a 5N aqueous solution of sodium hydroxide was added as a neutralizing agent in the formulation shown in Table 2, and ion-exchanged water was added under stirring to obtain a dispersion of polyester resin particles not containing a pigment. The obtained dispersion was kept in the four-neck flask and stirred while being kept at 60°C, and the pressure was reduced to distill off MEK. Then, after cooling to room temperature, ion-exchanged water was added and filtered through a 200-mesh wire net to obtain an aqueous dispersion d-1 of polyester resin particles not containing a pigment (solid content concentration 40.0%). The average particle size of the polyester resin particles not containing a pigment in the aqueous dispersion d-1 was 115 nm.

[0060] [Table 2]

[0061] Ink manufacturing example 1 The components were mixed according to the composition of the water-based ink shown in Table 3, and the resulting mixture was filtered through a membrane filter "Minisart" (manufactured by Sartorius) with a pore size of 1.2 μm to obtain water-based ink X1. The organic solvents, surfactants, and pH adjusters shown in Table 3 are as follows. [Organic solvents] BDG: Diethylene glycol monobutyl ether (Fujifilm Wako Pure Chemical Industries, Ltd.) PG: Propylene glycol (Fujifilm Wako Pure Chemical Co., Ltd. Reagent) [Surfactants] KF6011: Alkylene glycol modified polydimethylsiloxane (product name "KF-6011", manufactured by Shin-Etsu Chemical Co., Ltd., non-ionic surfactant) [pH adjuster] MDEA: N-methyldiethanolamine (Fujifilm Wako Pure Chemical Industries, Ltd.)

[0062] [Table 3]

[0063] Examples A1 to A8, B1 to B6, C1 to C6, D1 to D6, Comparative Examples 1 to 4 Each cleaning composition was prepared by heating and mixing the components shown in Tables 4 to 7 to 45° C., and then cooling to 35° C. Each cleaning composition was used to carry out the following evaluations. The results are shown in Tables 4 to 7. The components shown in Tables 4 to 7 are as follows. Solvent (A) Propylene carbonate (dipole moment: 5.64D): Reagent manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. Ethylene carbonate (dipole moment: 5.41D): Reagent manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. [Solvent (B)] (Solvent (B1)) Polyoxyethylene phenyl ether (average number of moles of EO added: 2.0): Nippon Nyukazai Co., Ltd. Polyoxyethylene phenyl ether (average number of moles of EO added: 2.3): Nippon Nyukazai Co., Ltd. Polyoxyethylene phenyl ether (average number of moles of EO added: 3.0): "Brownon PH-3" manufactured by Aoki Oil Industries Co., Ltd. Polyoxyethylene phenyl ether (average number of moles of EO added: 4.0): "Brownon PH-4" manufactured by Aoki Oil Industries Co., Ltd. Polyoxyethylene phenyl ether (average number of moles of EO added: 5.0): "Brownon PH-5" manufactured by Aoki Oil Industries Co., Ltd. Polyoxyethylene phenyl ether (average number of moles of EO added: 5.5): Nippon Nyukazai Co., Ltd. Polyoxyethylene benzyl ether (average number of moles of EO added: 2.0): Reagent manufactured by Tokyo Chemical Industry Co., Ltd. Ethylene glycol (dipole moment: 2.43D): Reagent manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. Diethylene glycol (dipole moment: 1.66D): Reagent manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. (Other solvents) Gamma-butyrolactone (dipole moment: 4.69D): Reagent manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.

[0064] <Cleaning ability> (Applying printing dots) Using the water-based ink X1 obtained in Ink Production Example 1, the ink was applied drop by drop (ink droplet volume per drop: 0.5 nL) at 5 mm intervals on a glass petri dish using a dispenser printing device to form a grid-shaped printed image having 5 vertical and 5 horizontal printed dots. The dispenser printing device used was a piezo jet dispenser "PICO Pμlse Valve SD" (manufactured by Nordson EFD), and the liquid body assembly used was "FLUID ASSY Pμlse MST 3.0S F0 E05" (opening 50 μm, ball size 3.0S). The dispenser was moved using "PRO4" manufactured by Nordson Corporation. (Cleaning test) Next, 2 g of each of the cleaning compositions of the Examples and Comparative Examples was added to the grid-shaped printed image on the petri dish, and after leaving it at room temperature for 5 minutes, it was shaken for 60 seconds at 100 rpm in a shaker, and the shaken petri dish was tilted 120 degrees to remove the cleaning composition from the petri dish. Next, 2 g of ion-exchanged water was poured into the petri dish, and after leaving it at room temperature for 1 minute, it was shaken for 60 seconds at 100 rpm in a shaker, and the shaken petri dish was tilted 120 degrees to remove the ion-exchanged water. (Cleaning evaluation) 25 printed dots of a grid-like printed image were observed, and the cleanability was evaluated based on the score (total cleanability score P) out of a total score of 100, based on the following criteria: if all the printed dots were removed, 4 points; if a thin transparent film remained, 3 points; if a thin colored film remained, 2 points; if some of the printed dots peeled off but some remained intact, 1 point; if there was no visible change in the printed dots, 0 point. A total cleanability score P of 80 or more indicates excellent cleanability.

[0065] <Material compatibility> The mass (M0) of about 0.08 g of an O-ring "BS007 Viton 5 / 32 inch" (material: fluorocarbon elastomer) (manufactured by RS Components Co., Ltd.) was measured as a resin part, and then the O-ring was immersed in each cleaning composition of the examples and comparative examples and stored at 60°C for one month. The resin part was then removed and immersed in 50 g of ion-exchanged water at room temperature for one hour. The resin part was then removed and dried overnight in an environment at a temperature of 60°C and a relative humidity of 10% or less, and then cooled for one hour in an environment at room temperature and a relative humidity of 50±10%, after which the mass (M1) was measured. The swelling ratio was calculated from the following formula using the calculated mass (M0) and mass (M1). If the swelling ratio is less than 20%, the compatibility of the part is excellent. Swelling ratio (%) = [(M1-M0) / M0] x 100

[0066] <Discharge recovery> (Continuous printing test before cleaning) In an environment of a temperature of 25±1° C. and a relative humidity of 10±5%, the water-based ink X1 obtained in Ink Production Example 1 was filled into a print evaluation device “OnePassJet” (manufactured by Tritec Corporation) equipped with an inkjet head “KJ4B-QA06NTB” (manufactured by Kyocera Corporation). The printing conditions were set as follows: head voltage 26 V, frequency 30 kHz, appropriate amount of ejected liquid 7 pL, head temperature 32° C., number of pre-ejection flushings 200, and negative pressure −4.0 kPa. Next, after printing for three consecutive hours without maintenance under the above printing conditions, a nozzle check pattern was printed and the number of nozzles where deflection or clogging occurred (number of missing nozzles before cleaning N0) was confirmed. Deflection of deflection was determined to have occurred when the ejection was deviated by 50 μm or more from the intended landing point. (Cleaning test) Next, 50 mL of each cleaning composition of the examples and comparative examples was injected into the inkjet head, and the cleaning composition was allowed to overflow from the nozzle side and washed while being poured. Next, the ink injection part of the head was plugged, and each cleaning composition was held in the head and left to stand for 5 minutes. After that, 50 mL of the same cleaning composition as the cleaning composition held in the head was further injected into the head and filled, and the cleaning composition was allowed to overflow from the nozzle side and washed while being poured. Finally, 1 L of ion-exchanged water was injected into the head and filled, and the ion-exchanged water was allowed to overflow from the nozzle side and washed while being poured. (Printing test after cleaning) In an environment of a temperature of 25±1° C. and a relative humidity of 10±5%, the ink X1 obtained in Ink Production Example 1 was filled into a print evaluation device “OnePassJet” (manufactured by Tritec Corporation) equipped with an inkjet head “KJ4B-QA06NTB” (manufactured by Kyocera Corporation). The printing conditions were set as follows: head voltage 26 V, frequency 30 kHz, appropriate amount of ejected liquid 7 pL, head temperature 32° C., number of pre-ejection flushings 200, and negative pressure −4.0 kPa. Next, a nozzle check pattern was printed under the above printing conditions, and the number of nozzles where deflection or clogging occurred (number of nozzle chips after cleaning N1) was confirmed. Deflection was determined to have occurred when the nozzle was deviated by 50 μm or more from the intended landing point. (Nozzle recovery rate) The nozzle recovery rate was calculated from the following formula using the number of chipped nozzles before cleaning N0 and the number of chipped nozzles after cleaning N1. A nozzle recovery rate of 90% or more indicates excellent ejection recovery, and a nozzle recovery rate of 95% or more indicates particularly excellent ejection recovery. Nozzle recovery rate (%) = [(N0-N1) / N0] x 100

[0067] [Table 4]

[0068] [Table 5]

[0069] [Table 6]

[0070] [Table 7]

[0071] It can be seen from Tables 4 to 7 that the cleaning compositions of the Examples are superior in cleaning properties and compatibility with components compared to the cleaning compositions of the Comparative Examples, and furthermore, when used as a cleaner for an inkjet head that ejects a water-based ink for inkjet printing, are superior in ejection recovery properties of the inkjet head.

Claims

1. A cleaning composition for an inkjet head, comprising a solvent (A) and water, The dipole moment of the solvent (A) at 25° C. as determined by a density functional method is 5.0 D or more; A cleaning composition for an inkjet head, wherein the cleaning composition has a water content of 30% by mass or more.

2. 2. The inkjet head cleaning composition according to claim 1, wherein the solvent (A) is at least one selected from the group consisting of propylene carbonate, ethylene carbonate, and sulfolane.

3. 2. The inkjet head cleaning composition according to claim 1, further comprising an organic solvent (B) having one or more groups selected from the group consisting of a hydroxy group and a polyoxyalkylene group.

4. 4. The inkjet head cleaning composition according to claim 3, wherein the organic solvent (B) comprises one or more solvents (B1) selected from the group consisting of ethylene glycol, diethylene glycol, polyoxyalkylene phenyl ether, and polyoxyalkylene benzyl ether.

5. The cleaning composition for an inkjet head according to claim 4, wherein the polyoxyalkylene group of the polyoxyalkylene phenyl ether or the polyoxyalkylene benzyl ether is a polyoxyethylene group.

6. 5. The cleaning composition for an inkjet head according to claim 4, wherein the polyoxyalkylene group of the polyoxyalkylene phenyl ether or the polyoxyalkylene benzyl ether is a polyoxyethylene group, and the average number of moles of ethylene oxide added to the polyoxyethylene group is 2 or more and 6 or less.

7. The inkjet head cleaning composition according to any one of claims 1 to 6, which is used for an inkjet head that ejects a water-based ink for inkjet printing, The ink-jet head cleaning composition for the water-based ink for ink-jet printing contains a polymer having an acid value of 5 mgKOH / g or more, and water.

8. Contains a solvent (A) and water, The dipole moment of the solvent (A) at 25° C. as determined by a density functional method is 5.0 D or more; The cleaning composition having a water content of 30% by mass or more is used as an inkjet head cleaner.

9. 9. The use according to claim 8, wherein the solvent (A) is one or more selected from the group consisting of propylene carbonate, ethylene carbonate, and sulfolane.

10. The use according to claim 8 or 9, further comprising an organic solvent (B) having one or more groups selected from the group consisting of a hydroxy group and a polyoxyalkylene group.

11. Contains a solvent (A) and water, The dipole moment of the solvent (A) at 25° C. as determined by a density functional method is 5.0 D or more; A method for cleaning an inkjet head using the composition having a water content of 30% by mass or more.

12. The method according to claim 11, wherein the solvent (A) is at least one selected from the group consisting of propylene carbonate, ethylene carbonate, and sulfolane.

13. The method according to claim 11 or 12, further comprising using a composition containing an organic solvent (B) having one or more groups selected from the group consisting of a hydroxy group and a polyoxyalkylene group.

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